1. Field of the Invention
This invention relates generally to field effect transistors, and particularly to a field effect transistor using a compound semiconducting substrate and a plurality of gates each connected in parallel.
2. Prior Art
As is well known in the prior art, field effect transistors usually include a low-resistance substrate such as a Si substrate. There is an active layer on the Si substrate. In the active layer, a gate region and a guard-ring as an isolation wall are formed, then, a source electrode, a drain electrode, and a gate electrode are arranged on the active layer. In such a structure of the field effect transistors, however, it is not known that a high-resistance substrate such as a GaAs substrate is used instead of the Si substrate.
Generally, junction capacitance between gate and source, gate resistance, and gate leakage current greatly influence the noise of field effect transistors. The present applicant company made a proposal relating to the above-mentioned field effect transistor having the GaAs substrate. In such a field effect transistor devised by the present inventors, since the guard-ring and the active layer are connected to each other, a large leakage current to the active layer results. Therefore, junction capacitance between the guard-ring and the active layer is also large thereby bringing about several disadvantages such as deterioration of high frequency characteristic and noise characteristic.